1. Field of the Invention
The present invention pertains to a method and system for measuring curvature in fluid transmission pipelines caused by heaving or subsidence of the earth's surface wherein a pipeline pig having distance and acceleration measuring devices on board is pumped through the line to measure changes in curvature of the line at predetermined locations.
2. Background
The monitoring of fluid transmission pipelines to determine movement of certain sections of the line as a result of subsidence, frost heaving and other movement of the earth's strata is an important environmental and economic consideration with respect to pipeline operation and maintenance. Periodic monitoring of changes of curvature of fluid transmission pipelines over the length of a particular pipeline segment is particulary important for pipelines extending through environmentally sensitive areas and areas of the earth which are subject to shifting or subsidence. Pipelines located in Arctic regions, for example, are more likely to be subjected to movement of the earth's strata as a result of heaving and subsidence of the earth during cyclical freezing and thawing. Other pipelines located in areas not capable of visual inspection, such as submarine installations, are also subject to shifting due to changes in river or ocean currents, storm surges, ice movement or unwanted engagement by ship anchors or the like.
The potentially disastrous environmental and economic consequences of severe pipeline displacement cannot be tolerated. Consequently, there have been several proposals for measuring changes in pipeline location including stadia techniques, acoustic emission and fiber optic methods. One proposal includes the provision of a pipeline pig carrying onboard an aircraft or marine type fully gimballed inertial guidance system. The aforementioned types of inertial systems typically require gyroscopic stabilization and are subject to error due to the necessity of correcting or recalibrating the stabilizing gyroscopes. In many pipeline applications, the length of the line and the required time for a curvature or displacement measuring pig to make a trip through the line is such that the stabilizing gyroscopes may introduce significant errors in the readings of the guidance system which cannot be corrected to give an accurate indication of actual pipeline displacement.
Accordingly, there has been an important need to improve on existing methods of measuring pipeline displacement due to earth subsidence, frost heaving and other causes of unwanted pipeline movement which have not been satisfied by existing types of pipeline monitoring methods and apparatus. It is to this end that the present invention has been developed with a view to providing an improved method and system for monitoring pipeline displacement or changes in curvature.